Superconducting ribbon



May 6, w69 E. R. scHRAl-DER 3,443,021

SUPERCONDUCTING RIBBON Filed April 28, 1967 INVNTOR @aff/JP .5M/m

' Arromu'r United States Patent 3,443,021 SUPERCONDUCTING RIBBON Edward Robert Schrader, Highstown, NJ., assignor to Radio Corporation of America, a corporation of Delaware Filed Apr. 28, 1967, Ser. No. 634,675 Int. Cl. H01b 7/34, I7/16 U.S. Cl. 174-126 13 Claims ABSTRACT 0F THE DISCLOSURE Background of the invention This invention relates to superconductors of generally ribbon shape.

To produce larger magnets of higher eld strength without adding turns thereto and thereby increasing the inductance of the magnet, the current carrying capacity and, therefore, the cross sectional area of the superconductive portion of a superconductive ribbon must be increased. For flexibility, and so that there will be less chance of cracking the superconductive portion of the ribbon when winding, the thickness of the superconductive portion of the ribbon must not become too great. Therefore, in winding larger magnets having progressively higher magnetic fields, it follows that the ribbon should be made progressively wider. However, the superconductive portion of the ribbon resists penetration by the magnetic field to which it is subjected, whereby the distribution of How of current through the ribbon is not uniform, the current flow being crowded away from the central portion of the ribbon and towards the edges thereof. Therefore, the maximum flow of current through the ribbon is reduced below the amount that would be expected if the current were distributed uniformly throughout the superconductive material.

To accomplish greater uniformity of current distribution in a superconductive ribbon, it has been suggested to deposit superconductive material on a ribbon shaped substrate of normal material and to etch away the superconductive material along a plurality of spaced lines parallel to the length of the ribbon, thereby to produce a superconductor in ribbon form comprising several superconductive paths in parallel. The magnetic field to which the ribbon is subjected can better penetrate such a ribbon. The current distribution in the ribbon tends to be equalized since the formation of the superconductive portion of the ribbon into separate parallel conductors prevents they current from crowding into the edges of the ribbon. The current carrying capacity of the ribbon so made is `increased over a ribbon having the same crossr sectional area of superconductive material and without the etched lines. However, etching a plurality of lines along a ribbon which may be narrow and of great length is a very expensive and a very slow process. Furthermore, it is advantageous `for the purpose of increasing the stability of magnets wound with superconductive ribbon to have shunt paths between parallel superconductive portions thereof.

It is an object of this invention to provide an improved superconductive ribbon.

It is a further object to provide a superconductor in ribbon form comprising a plurality of superconductors in parallel which can be made cheaply and more easily than known superconductors in ribbon form.

It is a still further object to provide an improved superconductive ribbon comprising several superconductive paths in parallel and also including shunt paths between said parallel paths.

Summary of the invention According to one embodiment of the invention, a superconductor in ribbon form is produced by grinding away the superconductive material deposited on a deformed substrate along a plurality of paths. In accordance with another embodiment of the invention the substrate is deformed to provide a mesh or expanded substrate and the superconductive material is deposited on some or all of the exposed surfaces of the deformed substrate, the superconductive ribbon so formed comprising a plurality of parallel paths and cross or shunt paths of superconductive material. In accordance with still another embodiment of this invention the deformed substrate may comprise separate parallel wires of normal material held in a side by side position by cross wires, superconductive material being deposited on the so formed substrate to provide a superconductive ribbon. A good conductor which does not become superconductive, such as silver or copper may be deposited on all of the exposed surfaces of the several superconductive ribbons so provided to provide stability in a known manner. Due to the gaps in the superconductive material, comprised by the ribbons so produced, the magnetic field to which the ribbons are subjected penetrate the ribbon to a greater extent than for a ribbon without gaps, whereby greater uniformity of the magnetic field in the vicinity of the ribbon as well as greater uniformity of current density in the various portions of the superconductive material of the ribbon is realized than in known superconductive ribbons, resulting in an increased current carrying capacity for the described superconductive ribbons. Furthermore, due to the openings in the superconductive ribbons so produced, the coolant, liquid helum, can be circulated through the holes in the ribbon, speeding up withdrawal of heat from the ribbon and thereby further stabilizing the magnet Wound with such ribbon. Furthermore, the mesh-like or perforated superconductive ribbons present shunt paths between the several longitudinal conductors of these ribbons, these shunt paths also further stabilizing the magnet wound by such ribbons.

Brief description of 'the drawing The invention will be better understood upon reading the following description in connection with the accompanying drawing, in which FIGURE l is a plan view of a superconductive ribbon in accordance with one embodiment of this invention,

FIGURE 2 is a cross section at an enlarged scale of the superconductive ribbon of FIGURE 1 along lines 2-2 of FIGURE 1,

FIGURE 3 is a cross section of a superconductive ribbon in accordance with a second embodiment of this invention,

FIGURE 4 is a perspective view of a superconductive ribbon in accordance with a third embodiment of this nvention,

FIGUR-E 5 is a plan view of a superconductive ribbon in accordance with a fourth embodiment of this invention,

FIGURE 6 is a partial cross section at an enlarged scale of the ribbon of FIGURE 5 along line 6 6 thereof,

FIGURE 7 is a plan view of a superconductive ribbon in accordance with a fifth embodiment of this invention, and

FIGUR-E 8 is a cross section at an enlarged scale of the ribbon of FIGURE 7 along line 8-8 thereof.

Description: of the preferred embodiments The ribbon 110 of FIGURES 1 and 2 comprises a deformed substrate tape 12 having ridges 14 along the length thereof and a layer of superconductive material l16 on the substrate 12 between the ridges 14, whereby the material 16 is continuous along the length of the ribbon and discontinuous in a circumferential direction. A layer of silver 18, which is continuous in all directions is deposited on the superconductive material 16 and on the edge portions of the ridges 14 ywhich extend through the superconductive material 16. This cross sectional configuration of the ribbon 10 may be produced by providing a substrate tape 12 comprising longitudinal ridges 14 and by providing an even coat of superconductive material on the substrate as by a vapor deposition process. The tape 12 may comprise stainless steel or any other suitable material. Then, the tape is ground flat, as by a grinding wheel to the point where the top of the ridges x14 are visible along their whole length through the remaining superconductive material 16. Due to this grinding step, the longitudinal ridges of superconductive material which had been deposited on the ridges 14 of the substrate will be ground away. Then the layer of copper or silver 18 is deposited on the resultant at ribbons as by electro-deposition. The completed ribbon 10 then comprises a plurality, fve in the example shown in FIG- URE 2, of separate superconductive paths comprising the superconductive material 16 between adjacent ridges 14. The magnetic 4field surrounding the ribbon 10` when current ows therein, will penetrate the substrate, whereby the current distribution in the ribbon will be more uniform than if the superconductive material 16 were continuous in the circumferential direction. Since the maximum current that a superconductor can carry in a given field is limited by the maximum current density in the superconductor, the ribbon of FIGURES l and 2 can carry more current without becoming normal than a ribbon having the same cross sectional area of superconductive material, but which is continuous in a circumferential direction. When the ribbon 10 is used, all the superconductive paths thereof will be connected in parallel. Therefore, when using such a superconductive ribbon, if one of the parallelly connected superconductive paths becomes normal momentarily for any reason, the other paths can carry the current otherwise carried by the normal path, the current being transferred to the other paths through the copper or silver layer, until the normal path again becomes superconductive. Therefore, a superconductive ribbon having a plurality of parallel paths connected in parallel increases the stability of a magnetic device, such as an electro magnet, wound with such a ribbon.

In the embodiment shown in cross section in FIG- URE 3, the substrate 22, which may also be stainless steel, may be provided as a flat tape, and longitudinal ridges 24 may be produced in the tape by so deforming the substrate as to produce longitudinal grooves 26 opposite the ridges 24, or the substrate tape 22 may be supplied with such ridges 24 and grooves 26 already therein. Then, the so deformed tape 22 may be coated with superconductive material 28 on all sides thereof, whereby ridges 30 of superconductive material will cover the ridges 24. Then the ridges 30 may be ground off as by grinding with a grinding wheel (not shown) and a layer of silver 32 is deposited on the superconductive material 28` and o'n the tips of the ridges 24 that extend through the superconductive material 28. While the outward appearance of the resultant completed ribbon 34 will be different from the ribbon 10, since longitudinal grooves 36 will be apparent along the length of the ribbon 34, the operation of the ribbon 34 is similar to the operation of the ribbon 10. However, since the substrate :22 on the ribbon 34 may be made from a flat thin tape, the ribbon 34 may be less expensive than the ribbon y10.

The ribbons illustrated in FIGUR-ES 4 and 5 are similar. They differ only in that FIGURIE 4 illustrates a superconductive ribbon 38 having a slotted substrate tape, and FIGURE 5 illustrates a superconductive ribbon 40 having an expanded substrate tape. Therefore, except for the substrates, the following description of FIGURE 5 will apply equally as well to FIGURE 4.

A coating of superconductive material 42 is applied to all exposed surfaces of the deformed substrate tape 44, which again may be of stainless steel (FIGURE 6), in a known manner. Then a coating of normal metal such as copper or silver 46 is applied to all exposed surfaces of the superconductive material 42. Since there are holes through the subtrate tape and therefore through the completed ribbons 38 and 40, a cooling fluid, such as liquid helium, as well as the magnetic eld produced by the current flow in the ribbons 318 and 40K may penetrate the ribbons 38 and 40. Also, due to the holes through the tapes 3-8 and 40, several parallel paths of superconductive material `42 exist along the length of the ribbons 38 and 40 and there are cross connections or shunts between these paths. While it is noted that the slotted holes through the ribbon 38 of FIGURE 4 and the diamond shaped holes through the ribbon 40 of FIGURE 5 overlap in the direction of the length of the ribbon, this overlap is not a necessary feature of these ribbons. Also due to the holes through the ribbons 38 and 40, the cooling effect thereon by the liquid helium bath is increased and the magnetic eld in the ribbon is more nearly equalized as compared to an imperforate ribbon, whereby the ribbons 38 and 40 are cooled more efficiently and carry more current without becoming normal than a similar imperforate ribbon having the same cross sectional area of superconductive material. Furthermore, the cross connections or shunts provide shunt paths around any portion of the superconductive ribbon that may become normal momentarily for a long enough period so that the normal portion may again become superconductive, whereby the cross connections or shunts of the ribbons of FIGURES 4 and 5 lidd stability to an electromagnet wound with such rib- Turning to FIGURES 7 and 8, the substrate tape for the ribbon 52 comprises a mesh or screen which, as shown, may be a woven mesh or screen. The mesh, as illustrated in these figures comprises a plurality of parallel wires 54, which comprises the warp, of a material that does not become superconductive, and a plurality of transversely positioned cross wires 56, which comprises the weft, of similar material. The wires 54 and S5, like the substrates 12, 22 and 44 may be of stainless steel. Only three of the cross wires are shown in FIGURE 7, however along the length of the substrate tape the number may be very large. The wires 54 and 56 may be welded together at their crosspoints. On the substrate tape comprising the woven wires 54 and 56, a coating of superconductive material 58 is applied, and on the surface of superconductive material 58 a coating of copper or silver 60 is applied. The superconductive ribbon 52 provides parallel superconductive paths 'by means of the superconductive material on the wires 54 and the ribbon also provides cross paths or shunts around any section of the superconductive paths that may become normal by means of the superconductive material on the cross wire 56. Furthermore, openings appear through the ribbon S2 between the coated wires 54 and 56 for the penetration by the cooling fluid and by the magnetic field to which the ribbon will be subjected. Thereby, the ribbon 52 exhibits the advantages of easier cooling discussed in connection with the ribbons 38 and 40 and also of the greater current carrying capacity discussed in connection with the ribbons 10, 34, 38 and 40. Furthermore, each of the ribbons 10, 34, 38, 40 and 52 exhibits exibility in a direction perpendicular to the plane thereof.

The superconductive material may be deposited on the several deformed substrates of FIGURES 4 through 8 by vapor depositions. Use of the perforated substrates of FIG- URES 4 through 8 results in a more even flow of the gas or vapor in the vicinity of the substrate during the deposition process. Therefore, better control of the vapor deposition on the deformed substrates of the ribbons 38, 40 and 52 is possible than with imperforate substrates. Furthermore, the screen-like ribbon 52 provides other advantages, such as ease of cutting the ribbon 52 longitudinally to provide ribbon of various widths, whereby only wide ribbon need be stocked. Also, since the wires 54 and 56 are round, the crystal superconductive material will be deposited thereon in all orientations perpendicular to the length of the wires 54 and 56 thereby eliminating variations in the critical current of the ribbon 52 as the direction of field through the ribbon 52 is changed. This advantage is also present, but not to quite such a great degree, in the perforate ribbons 38 and 40, since the superconductive material is deposited on the edges of the perforations, that is on the walls of the holes through the ribbons 38 and 40. Due to the perorations through the ribbons 38, 40 and 52, the exibility of these ribbons is increased and these ribbons may `be more easily shaped to t on an irregular surface upon which they are to be positioned than imperforate ribbons.

Modifications of the above described superconductive ribbons may occur to a person skilled in the art. Therefore, the above description is to be considered as illustrative and not in a limiting sense.

What is claimed is:

1. A flexible superconductive ribbon comprising a deformed substrate of normal flexible metallic material having length along a longitudinal direction and superconductive material coated on said substrate in such a manner as to provide a plurality of superconductors which are continuous in said longitudinal direction and discontinuous in a first direction transverse to said longitudinal direction, and normal metal coated on said superconductive material.

2. A superconductive ribbon according to claim 1 in which said deformed substrate comprises longitudinally directed ridges, and said superconductive material is positioned on said substrate between said ridges.

3. A superconductive ribbon in accordance with claim 1 in which said deformed substrate comprises a tape having a plurality of openings therethrough, said openings having a long and a short dimension, the long dimension of said openings being parallel to said longitudinal direction of said ribbon.

4. The superconductive ribbon of claim 1 in which said substrate comprises a slotted tape, said slots being arranged in columns and extending along the longitudinal direction of said superconductive ribbon.

5. A superconductive ribbon of claim 1 in which said substrate comprises a slotted tape, said slots being arranged in columns extending along the longitudinal direction of said superconductive ribbon and in which said slots in adjacent columns overlap.

6. A superconductive ribbon in accordance with claim 1 in which said substrate comprises expanded material.

7. The superconductive ribbon in accordance with claim 1 in which said substrate comprises a mesh,

8. The superconductive ribbon in accordance with claim 1 in which said substrate comprises a rst plurality of wires extending along said longitudinal direction and a second plurality of wires extending transversely to said first plurality of wires, said second plurality of wires being fixed to said first plurality of wires.

9. The superconductive ribbon as expressed in claim 1 and including a plurality of shunt superconductive paths extending in a second direction transverse to said longitudinal direction and joining said plurality of superconductors.

10. A exible superconductive ribbon comprising a deformed iiexible, normal, metallic substrate having length along the longitudinal direction and having openings therethrough which extend in columns parallel to said longitudinal direction, superconductive material deposited on all exposed surfaces of said substrate and normal metal deposited on said superconductive material.

11. The superconductive ribbon in accordance with claim 10 in which said substrate is of slotted material.

12. The superconductive ribbon as expressed in claim 10 in which said substrate is of expanded material.

13. A superconductive ribbon in accordance with claim 10 in which said substrate is of mesh material.

References Cited UNITED STATES PATENTS 361,550 4/1887 Scarles 117-99 X 1,641,374 9/1927 Chryst. 2,335,494 11/1943 Fay 117-98 X 3,249,686 5/1966 Paar 174-117.2 3,300,746 1/1967 Franz 174--15 X 3,372,470 3/1968 Bindari.

FOREIGN PATENTS 233,050 4/ 1925 Great Britain.

OTHER REFERENCES American Institute of Physics Handbook 2nd Edition McGraw Hill, N.Y. 1963, ppt. 9-112.

LEWIS H. MYERS, Primary Examiner. E. A. GOLDBERG, Assistant Examiner.

U.S. Cl. XR. 174-15, 117; 335-216; 117-212, 210, 99; 29-194 

